The enzyme Elongation Factor 2 Kinase (eEF2-K) belongs to a novel family of protein kinases, with prototypical member being Dictyostelium myosin heavy chain kinase A (MHCK A), which display no homology to conventional eukaryotic protein kinases. This protein kinase is highly specific to Elongation Factor 2 (eEF2) and is responsible for eEF2 phosphorylation. eEF2 promotes ribosomal translocation, the reaction that results in the movement of the ribosome along mRNA during translation. eEF2 was identified among the most prominently phosphorylated proteins in crude tissue and cell lysates. Importantly, it was found that phosphorylation of eEF2 arrests translation, suggesting that this may be a critical mechanism by which the rate of protein synthesis is regulated (Ryazanov, A. G. (1987). Ca2+/calmodulin-dependent phosphorylation of elongation factor 2. FEES Lett 214, 331-334; Ryazanov, A. G., Shestakova, E. A., and Natapov, P. G. (1988).)
The activity of this kinase is increased in different types of cancers and may be a valid target for anti-cancer treatment. For example, it has been reported that eEF2-K is overexpressed in breast cancer cell lines and tumors with little or no activity observed in normal breast tissue. Moreover, there is evidence indicating that the enzyme is activated in rat glioblastoma (Chang et al, (1995) Calmodulin-dependant protein kinases in rat glioblastoma, Cell Growth Diff.) The natural product rottlerin has been shown to inhibit growth of glioma cell lines by inhibiting eEF2-K. Parmer et al, (1997) Cell Growth Differ. Vol. 8, 327)).
This enzyme was also shown to have increased activity in human brains of individuals with AD (Li, X., Alafuzoff, I., Soininen, H., Winblad, B., and Pei, J. J. (2005) Levels of mTOR and its downstream targets 4E-BP1, eEF2, and eEF2 kinase in relationships with tau in Alzheimer's disease brain. FEBS J.272, 4211-4220) although the mechanism and relevance of the enzyme for such purposes was not clear. Accordingly, eEF2 kinase inhibitors could be used to modulate the pathophysiology of a number of disease states including brain cancer, breast cancer, ischemic heart disease, etc.
It was recently discovered that inactivation of a ubiquitous cellular enzyme eEF2 kinase can confer resistance to radiation by suppressing radiation-induced apoptosis. Mucosal damage, such as the damage to the intestine is a major dose-limiting event in radiation therapy and chemotherapy. Aspects of rapid cell turnover, distinct compartmentalization of damage, and known differentiation pathways of crypt cells in the murine and human intestine have been well studied. Treating such conditions have been the subject of an ongoing research. Various modalities, such as antioxidant therapy and inhibition of serotonin activity at the gastric level, have been suggested and employed in the art. However, there is still a need to mitigate side effects associated with drug and radiation therapy.
Until now all alpha kinase phosphorylation sites in protein substrates identified fall within the structural class of alpha helices (Drennan and Ryazanov, 2004). It has been unclear whether these kinases have primary sequence specificity dictated by residues that surround the site of phosphorylation, or whether substrate recognition is mediated principally by secondary structure. Accordingly, there is a need in the art to clarify this issue as a means for developing targeted active ingredients.